make Grid.set_e throw out of bounds errors

src/grid.ml

@@ -30,7 +30,12 @@ let at_e (grid : 'a t) (point : Vec2.t) =
   Option.get_exn_or "point out of bounds!" @@ at grid point
 ;;
 
-let set_e grid point item = Array.set grid.items (idx_of_vec2 grid.width point) item
+let set_e grid point item =
+  if in_bounds grid point
+  then Array.set grid.items (idx_of_vec2 grid.width point) item
+  else failwith "point out of bounds!"
+;;
+
 let ( .%() ) = at_e
 let ( .%()<- ) = set_e